1. Field of the Invention
This invention relates to resin compositions for the fabrication of LCD (liquid crystal display) color filters and image-scanning color separation filters, printing inks for the fabrication of such filters, and optical filters obtained using such inks.
2. Description of the Related Art
Numerous proposals have been made for the fabrication of heat-resistant color filters by using a resin composition of a polyamic acid as a precursor of a polyimide and a colorant such as a dye or pigment added thereto (for example, Japanese Patent Laid-Open No. 46325/1983, Japanese Patent Laid-Open No. 254906/1986, Japanese Patent Laid-Open No. 234104/1987, etc.). According to a process for producing a colored optical filter by using such a resin composition, a coating is first formed on a base material by such a coating technique as spin coating, roll coating or printing, and the base material with the coating formed thereon is then heated usually to 250.degree. C. or higher, preferably to 300.degree. C. or higher so that the polyamic acid is dehydrated and imidated. A polyamic acid is however thermally unstable in general. If a polyamic acid is left over in the form of a solution, its molecular weight may decrease, or gelation may proceed so that the solution may no longer be a homogeneous solution. This makes it difficult to form the above-described coating. As the above-mentioned heating is conducted at such a relatively high temperature, the dye or pigment is prone to pyrolysis or sublimation during the heating, leading to failure in obtaining a color filter of desired spectral characteristics in some instances.
Polyimide resins are generally known as heat-resistant resins. No technique was however known in the past for the fabrication of a filter by direct coating of a polyimide resin composition on a base material.